"ATP"

Figure 5. Experiments suggesting rotation of the F₁ subunit of the ATP Synthase complex found in the bacterial outer membrane.

(1) The F₁ hexamer was anchored to a glass slide by attaching 6 histadine residues (# 1) to each b subunit.
(2) The glass slide was coated with a metal reagent that binds histadine, and the b subunit was attached to the slide.
(3) The g unit (# 2) was modified so that it would bind a molecule of actin (# 3), a long, linear protein of muscle.
(4) The actin molecule in turn, was modified by attachment of a molecule that fluoresces in ultraviolet light (# 4). Thus the movement of the g unit could be monitored directly in the light microscope with a uv light source, even though the whole assembly is exceedingly small.
(5) When ATP was added to the anchored F₁ subunit, the fluorescent marker was seen to rotate in discrete 120 degree increments. During the synthesis of ATP, rotation of the g unit by the proton motive force acting on the F₀ complex would therefore generate ATP. [after H. Noji et al., 1997, Nature 386:299; and R. Yasuda et al., 1998, Cell 93:1117]

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